This invention relates to brake systems for vehicles and the like and pertains more particularly to an improved emergency brake system for use in association with dual fluid operated service brakes to effect the automatic application of the emergency brake upon the application of the service brakes when a hydraulic failure occurs in one of such service brakes.
Many heavy duty vehicles, such as wheel loaders and the like, have a hydraulic service brake for each of its wheels and a separate drive line mounted emergency brake. In vehicles of this type, it is common practice to use an air-over-hydraulic service brake system which has a pair of air actuated master cylinders for applying separate ones of the wheel brakes, such as one master cylinder for the front wheel brakes and the other for the rear brakes. Also, the emergency brake is usually constructed so as to be spring applied and air pressure released so as to be automatically applied whenever air pressure is lost or becomes insufficient to apply the service brakes. The service brake system is normally controlled by an operator by a treadle or foot pedal operated valve located in the operator station, whereas the emergency brake is normally controlled manually by a lever or button operated emergency valve.
The main problem with such prior art brake systems is that there is no connection between the hydraulic portion of the service brake system and the emergency brake to effect the application of the emergency brake when an abnormal condition in such hydraulic portion occurs. Consequently, the operator would not be aware of a hydraulic failure in the service brake system until he had attempted to apply the service brakes and found them ineffective. In order to correct such a situation, he must then reach for and apply the emergency brake control, which is quite time consuming. Thus, it would be desirable to provide an emergency brake system which would automatically apply the emergency brake in the event of a hydraulic failure in the service brake system so as to eliminate the delay between the discovery of such failure and the manual application of the emergency brake by the operator.